I think the explanation was not quite right.
Time Machine takes backups every hour. So after a day, you have 24 backups. As these backups get older, it keeps one and throws away the other 23 hourly backups. After a month you have 24 hourly backups of the last 24 hours, plus 30 daily backups. As the daily backups become older than 30 days, Time Machine throws away six out of every seven weekly backups.
So you always have: Hourly backups of the last 24 hours. Daily backups of the last 30 days. Weekly backups as long as your hard drive space lasts.